Officials with the Ontario Environment ministry will assess whether the runoff from a toxic fire Saturday morning poses a health risk. The car-yard blaze drew in dozens of firefighters and curious onlookers as smoke billowed into the sky.

The three-alarm blaze took place just east of the Canada Science and Technology Museum, at a steel facility called ArcelorMittal -- formerly known as Baker Bros. Iron & Metal.

An acrid-smelling, 100- to 150-foot smoke plume towered above the facility, visible as far as 35 kilometres away.

Breathing masks required

Starting at 9:30 a.m. in a pile of crushed cars behind the facility near Highway 417 and Innes Road, firefighters donned special breathing appratuses to fight their way through the toxic fumes created by burning car tires and upholstry.

It took two hours before they began to gain the upper hand. In the meantime, 16 rigs and 45 firefighters gathered near the 30-foot long, 30-foot wide, and 10-foot high pile of discarded vehicle debris, hosing the area with water and monitoring it for hotspots.

"The flames were coming out all over," said onlooker Ralph Lepensee. "They had to back up the firemen on the ladders . . . there were explosions."

Officials were expected to remain on scene all day Saturday, possibly into Sunday morning to fully quench the flames.

Residents drawn from outlying Ottawa areas

In the roads nearby the blaze at 2555 Sheffield Rd., CTV Ottawa spoke with curious residents who arrived from Kanata, Greely and Barrhaven after spotting the dark cloud.

Acrid stenches drifted over the neighbourhood; as nearby resident Matthew Lemieux remarked, "It smelt like burnt rubber and burnt plastic throughout the street . . . you can smell it everywhere."

At one point, onlookers could hear an explosion -- what one person described as a gunshot sound. It was due to car shocks exploding in the intense heat, said Mark Messier from Ottawa Fire Services.

No damage amount is yet estimated. By late morning, the smoke turned from dark black to a much lighter hue, which fire officials said meant the fuel source for the fire was diminishing.

Road closures remained all day at Sheffield and Walkley roads, as well as the Leeds Avenue and Bantree street intersections. The fire remains under investigation.

Firm specializes in steel products

ArcelorMittal's branch in Ottawa is among several facilities stretching through 60 countries; the firm specializes in steel fields such as automotive, household appliances and construction.

As of 2009, the company's website said, as a whole it produced revenues of $65.1 billion and had a crude steel production of 73.2 million tonnes -- around eight per cent of what the world produces.

The company's first-quarter results were released in late April, falling short of investor expectations as iron ore prices rose and construction projects decreased.

Earnings were around $1.9 billion, down 11 per cent from the last quarter of 2009 and falling $2 million short of where the market expected they would be.

The firm noted it expects demand will rise 60 per cent in the next three months, pushing earnings to between $2.8 billion and $3.2 billion, as the global recession eases.

With a report from CTV Ottawa's Kate Eggins